The present invention relates to methods of treating gases using pressure and temperature swing adsorption, or temperature swing adsorption, together with apparatus and materials for use therein. Particularly the method is directed at purification of gases by removal of particular components therefrom, and the regeneration of adsorbent materials in the apparatus used for the method.
The requirements of an adsorbent system for cyclic filtration processes are not comparable with those of conventional single pass filters. This is because the metallic impregnants on such filters are an undesirable feature as they promote chemisorption. For maximum performance and service life cyclic filtration must therefore proceed reversibly by physical adsorption. Furthermore, the regeneration step must not result in adsorbent degradation; thermal aging, which can result from overheating of the filter bed, being just one example of such adsorbent degradation. In addition to these considerations, other factors such as particle size and hardness must be assessed when selecting adsorbents for PTSA applications.
Air purification processes. such as those required in collective protection situations wherein air from an external source is purified before delivery to an enclosed area occupied by personnel, typically consist of three stages each requiring a different adsorbent material; (i) removal of high boiling contaminants (e.g. boiling point over 50.degree. C.), (ii) removal of water vapour, and (iii) removal of low boiling contaminants (e.g. boiling point below 50.degree. C.). The distinction between high and low boiling contaminants in terms of exact temperature range is not important; the critical requirement is the removal of contaminants having a boiling point between approximately -90.degree. C. and 200.degree. C.).
The identification of an adsorbent for cyclic filtration of high boiling components is especially demanding as such components are generally strongly physically adsorbed and may be irreversibly retained. Adsorbent characterisation using nitrogen adsorption will elucidate the porous characteristics of an adsorbent but are not useful in prediction of adsorption and regeneration properties; adsorption and desorption data for dimethylmethylphosphonate, ethandiol and a range of other high boiling simulants provides more useful data in this regard.
Using such volatile materials the present inventors have studied a variety of adsorbents and determined that, although many of these have high adsorption capacity, in order for a filter bed to be adequately regenerable only certain types of adsorbent materials meet operational requirements.